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Subsequent Events Subsequent Events (Details) (USD $) In Millions, unless otherwise specified | 0 Months Ended |  | 0 Months Ended
--- | --- | --- | ---
Jul. 15, 2014 MDU Resources Group, Inc [Member] | Apr. 15, 2014 MDU Resources Group, Inc [Member] | Feb. 10, 2014 MDU Resources Group, Inc [Member] | Jan. 27, 2014 MDU Energy Capital [Member]
Subsequent Event [Line Items] |  |  |  |
Senior notes issued | $ 100.0 | $ 50.0 |  | $ 30.0
Senior notes weighted average interest rate | 4.60% | 4.60% |  | 5.30%
Purchase Price of Acquisition |  |  | $ 183.0 |

X
- Definition Purchase price of acquisition subsequent to date of financial statements. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Describes the event or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition Describes the event or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued. + References No definition available. + Details
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Namespace Prefix: | mdu_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
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